[Asterisk-Users] Disconnect supervision question

[James Fogg]

I'm trying to use Asterisk as a voice mail system and all is going well
except for one issue. When the outside caller drops the connection
Asterisk doesn't sense it. It keeps the line open for about 2 minutes
before dropping it. The FXO is attached to a key system (hybrid PBX).
There was a home-type digital answering machine previously on the same
extension and it was able to sense disconnect without any problems.

The interface is a non-Digium single port FXO card (modem) with R13 &
R19 removed to mimic the Digium card. The software is the current
release of Asterisk at home from ISO format (self booting CD that does an
OS install and Asterisk compile automagically).

My question is if Asterisk has settings to control disconnect sense, or
do I have to look at the key system (hybrid PBX) that it's attached to. 

 -James